For a conventional three-dimensional shape measuring apparatus, a light-section method is used which is to: irradiate an object with a laser slit beam, capture a positional relationship of the slit beam on the object using a camera so as to measure a distance from the object, and reconstruct a three dimensional shape of the object. Another method is a volume intersection method which is to estimate an outer shape of the object by installing cameras all round the object so as to eliminate blind spots and superimposing silhouettes three-dimensionally, based on a silhouette image of the object captured by each of the cameras and the camera position.
In performing three-dimensional reconstruction of the object according to the above method, the reconstruction becomes more accurate when more cameras are used. However, since it is necessary to perform calibration on each of the cameras, there is a contradiction that it becomes more difficult to perform calibration when more cameras are used.
Thus, as a technique to reduce the number of cameras while at the same time maintaining the accuracy, it is possible to consider capturing, using a single camera, images of both the front and a blind spot for the camera by reflecting the blind spot in a mirror so as to perform three-dimensional reconstruction on the blind spot. As a practical method for obtaining an image of the blind spot using the mirror, one of the suggested techniques is to: first, measure a visible portion of the object by the light-section method, and cut out only the blind spot reflected in the mirror with reference to the coordinates of the object and the known coordinates of the mirror, so as to obtain the result of the three-dimensional reconstruction of the blind spot.